MU5

The commercial failure of the Atlas didn’t put a stop to Manchester’s pioneering efforts. They moved on, in 1966, to an almost legendary machine - the MU5, Manchester University 5. Although perhaps not as revolutionary as MUSE, the MU5 brought all of the ideas together in an advanced and modern machine. It was built using integrated circuits - but not the LSI do-everything chips we use today. The MU5 used ECL, Emitter Coupled Logic which crammed only a few tens of transistors on each chip but it had the advantage of being fast. The MU5 was twenty times faster than the Atlas but it wasn’t just a faster version of the old machine. Experience of the Atlas changed the designers’ ideas of how things should be done. For example, there was now only one general purpose register. Variables were automatically cached in a 32 line fully associative cache. This allowed the compiler writers to ignore the problem of register assignment. It was highly pipelined - the ALU used a five-stage pipe with a 50ns operation time for each stage. It also had branch prediction - something we have only just seen introduced in the Pentium. It’s memory organisation was also advanced - a segmented paged design that hid the actual physical structure of the memory from the programmer.

The MU5 in use

With the sale of Ferranti’s computer business to ICT it fell to them to help with the MU5 project and they based their 2900 series machines on the MU5. So while there was only ever one MU5 its ideas lived on in the 2900 and in many other machines. It was the last of the Manchester computers - switched on in 1974 for general use it worked until 1979. When Kilburn retired there was an MU6 project but never an MU7 or 8. The era of building large mainframe computers was almost at an end and it was time for the integrated circuit designers to see how much of the best could be squeezed onto a single chip.

The MU5 on its way out...

Finally you might like to know how these super computers, the Atlas and the MU5, stand up against our current desktop machines. It isn’t an easy comparison because these two machines were both asynchronous, i.e. the didn’t work at a fixed speed. The Atlas had 96Kbytes of RAM and could manage about .6 MIPS fixed/floating point adds. The MU5 had 128Kbytes and could manage about 20MIPS fixed point adds and 4MIPS (floating point adds). Not really at all super by today's desktop standards but we had to start with something...

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